Turbidity is an optical property of fluids, and is proportional to the amount of particles that are suspended in the fluid to scatter light passing through the fluid.
For example, in environmental tests such as water examination and clinical tests such as a test using immune turbidity, it is necessary to measure the turbidity of liquids.
For instance, in a clinical test, antigens can be detected from a sample solution by measuring variations of the turbidity of the solution since the turbidity of the solution increases due to antigen-antibody reactions.
Turbidity can be measured using a turbidimeter (also, called a nephelometer) that casts one or more laser beams or white light beams through a vessel containing liquid and measures the intensities of the beams transmitted through the vessel or scattered by the liquid. In this way, the turbidimeter can measure the turbidity of the liquid.
When the turbidimeter uses at least two beams, the turbidimeter can measure turbidity more precisely with a low influence of noise, by comparing the intensities of transmitted or scattered beams.
The arrangement of the optical components of the turbidimeter can be adjusted to reduce optical noise caused by light reflected or scattered from a vessel wall or other optical components to an optical detector.
In such a turbidimeter, a laser or white light beam emitted from an optical system passes just once through a vessel containing a test solution.
That is, since a scattering of the beam is measured while the beam passes through the solution once, it is difficult to measure the turbidity of the solution when the amount of the solution is not sufficiently large or the particle concentration of the solution is low.